Fuel cells have been proposed as a power source for electric vehicles and other applications. One known fuel cell is the proton exchange membrane fuel cell (PEMFC) that includes a membrane electrode assembly (MEA) comprising a thin, solid polymer membrane-electrolyte having an anode on one face of the membrane electrolyte and a cathode on the opposite face of the membrane-electrolyte. The MEA is sandwiched between a pair of electrically conductive fluid distribution elements which serve as current collectors for the anode and cathode. Flow fields are provided for distributing the fuel cell's gaseous reactants over surfaces of the respective anode and cathode. The electrically conductive fluid distribution elements may themselves form a part of the flow field in the form of appropriate channels and openings therein for distributing the fuel cell's gaseous reactants over the surfaces of the respective anode and cathode.
In a fuel cell, the gaseous reactant at the anode preferentially comprises a fuel stream of pure H2. An alternative to using pure H2 as the gaseous reactant is to use a reformate fuel stream that is produced by converting a hydrocarbon-based fuel such as methanol or gasoline. This reformate fuel stream, in addition to containing H2, also contains impurities such as carbon dioxide (CO2), nitrogen (N2), and carbon monoxide (CO). For fuel cells operating at temperatures below 200 C, and especially for the PEMFC operating at temperatures around 100 C, it is known that CO, even at levels of 1-10 ppm, severely degrades a platinum electrocatalyst present in the anode and cathode electrodes. This degradation leads to a significant reduction in fuel cell performance, and is even more pronounced at the lower operating temperatures that are desirable.